The present invention relates to a rack and pinion feed for feeding strip stock into a machine, such as a press, and in particular to a motorized feed length adjustment mechanism therefor.
In order to feed sheet metal from supply rolls into a mechanical press, it is common practice to pinch the material between a pair of opposing feed rolls and drive the feed rolls in intermittent fashion in synchronism with the press by means of a power take-off from an extension of the press crankshaft extending out the the crown of the press. One such type of feed mechanism is known as a rack and pinion feed wherein an eccentric arm connected to the crankshaft extension is connected to a rack and pinion drive mechanism by a connecting rod. Such rack and pinion feed mechanisms are well known and have been in widespread use for many years.
In early feeds of this type, when it became necessary to adjust the stroke of the connecting rod in orer to change the length of material fed into the press on each cycle of the feed, it was necessary to stop the press and manually adjust the extent of movement of the crank arm. Since the adjustment mechanism is typically located coaxial with the crankshaft of the press, it was often necessary for the person to mount a ladder or scaffold to reach the adjustment mechanism. This operation proved to be quite cumbersome and time consuming, because it was often necessary to make a number of fine adjustments to attain the desired length of feed, with the necessity of again starting the press between each adjustment so that the change in feed length could be measured.
In order to enable adjustment of the feed length while the press was running, a number of motorized adjustment mechanisms were developed. One such adjustment mechanism employed an electric motor which rotated the feed screw or other threaded adjustment element through a rather large and complicated gear box. In addition to the large size and complexity of the gear mechanism which was needed to reduce the speed of the motor down to the slow speed necessary to make fine adjustments in the eccentric length, the electrical connections between the stationary and rotating portions of the feed necessitated the use of slip rings and brushes. The buildup of static charge on the slip rings often created false signals which caused the adjusting mechanism to move out of the position in which it was set. Additionally, the inherent overdrive characteristic of an electric motor does not permit the motor to be started and stopped with the degree of precision needed to make very fine adjustments.
Another type of adjusting mechanism for a rack and pinion feed employs a pneumatic motor to rotate the lead screw and an air cylinder to lock the slide against the block once the desired eccentric length is reached. An example of this type of adjustment mechanism is disclosed in patent 3,485,080, but has the disadvantage that the mechanical connections between the air motor and locking cylinder are quite complicated, thereby increasing manufacturing and maintenance costs.